The use of soluble Ziegler-Natta type catalysts in the polymerization of olefins is well known in the art. In general, such systems include a Group IV-B metal compound and a metal alkyl cocatalyst, such as an aluminum alkyl cocatalyst. More broadly, it may be said to include a mixture of a Group I-III metal alkyl and a transition metal complex from Group IVB-VB metals, particularly titanium or zirconium with aluminum alkyl cocatalysts.
Lewis acid cocatalysts such as aluminum alkyls and methylalumoxane are ubiquitous components of several important classes of highly active group alkyl-based (e.g., titanocene, zirconocene) olefin polymerization catalysts. Although electrodialysis, chemical trapping, model synthetic, XPS, surface chemical, NMR spectroscopic, and theoretical studies argue indirectly that the role of the Lewis acid is to promote (e.g., by alkide abstraction) the formation of unsaturated "cation-like" active centers (e.g., Cp.sub.2 MR.sup.+, where Cp=C.sub.5 H.sub.5), the exact structural nature of the catalyst-cocatalyst interaction has remained elusive.
While Ziegler-Natta type catalysts are in wide use, a continual effort is expended to improve on such catalysts to obtain better control over molecular weight and molecular weight distribution; to reduce the use of excess cocatalyst; and to permit the synthesis of small oligomers having a specific molecular weight.
Homogeneous cationic Group IV metallocene-type of complexes with the general formula L.sup.1 L.sup.2 MR.sup.+ X.sup.- (L.sup.1 and L.sup.2 are (substituted) cyclopentadienyl type ligands; M=Ti, Zr, Hf; R=H, Alkyl; X.sup.- is a "non-coordinating", anion derived from B(C.sub.6 F.sub.5).sub.3, B(C.sub.6 F.sub.5).sub.4 or methylalumoxane) have been studied extensively as olefin polymerization catalysts. Compared to traditional Ziegler-Natta catalysts, these metallocene-type catalysts have much better defined structures and chemical "tunability". For .alpha.-olefin polymerizations, the molecular weight is strongly modulated by the electronic and steric environment of the ligands.
Group IV metallocene-based .alpha.-olefin dimerization catalysts are known to include the use of metallocenes substituted and unsubstituted with alumoxanes methylalumoxane and other alkylalumoxanes, aluminum alkyl halides and a carborane anion as the cocatalyst.